Problem:

• My record-triggered flows that contain a Plauti apex action don't work anymore.
• When creating a record-triggered flow with a Plauti apex action, it will not save.

It is suggested to place the action in an asynchronous or scheduled path, but I want to use it in a synchronous path.
The error messages state:

“You must place this action in an asynchronous path. Add an asynchronous path in the Start element.”
“A record-triggered flow's Run Immediately path can't execute transaction-controlled actions. Remove this element from the flow, or move it to a scheduled path."

Answer:

From Salesforce’s Winter ‘26 release onward, it appears like flow apex actions in record-triggered flows cannot be used anymore in an immediate path (synchronous path or non-scheduled path). 
Note that screen flows and auto-launched flows are not affected.

To still use Plauti apex actions in an immediate path, change the flow's Transaction Control settings to Always continue in current transaction.

Alternatively, you can use an asynchronous or scheduled path, but for most Plauti apex action purposes this is not an option.

Read more about this Salesforce flow change in https://help.salesforce.com/s/articleView?id=005167102&type=1.